Handles of small-scale electrical appliances such as toothbrushes or shavers usually fulfil a double function. On the one hand, the handle forms the grip at which the appliance is gripped by a user's hand to control the orientation and to move the working tool of the appliance such as the brush head over the teeth. On the other hand, the handle usually receives at least a part of the drive unit for driving the working tool of the appliance, wherein often an electric motor, the batteries for powering the motor, a transmission for transmitting the motor's rotation to the working tool and a control unit are received in the handle.
The minimum size of the handle is therefore determined by the size of the drive unit and the space required for receiving the drive unit. Consequently, in order to reduce the size of the handle and to reduce the diameter thereof, it has been tried to reduce the size of the drive unit to achieve good handling and nice ergonomic appreciation of the handle. On the other hand, as the size reduction of the drive unit is expensive and still limiting, it is desirable to make the housing surrounding the drive unit as slim as possible for a given size of the drive unit. In order to achieve this, an intelligent design of the housing is necessary so as to utilize the interior space of the housing as far as possible to accommodate the drive unit's components.
Prior art toothbrushes usually have a handle forming a tube-shaped housing consisting of two or more housing parts which are connected at end portions thereof. In order to achieve a waterproof or water-resistant sealing of the interface of the housing parts, the housing parts are designed to overlap each other so that the end portion of a first housing part having a smaller diameter can be inserted into the end portion of the other housing part having a larger diameter. The overlapping end portions may be provided with threads so that the housing parts can be connected to each other by means of screwing them together. Such screw-type connection between the housing parts allows for easy sealing the housing part's interface in a waterproof manner, as an elastic sealing ring can be placed between the housing parts and press against step-shaped contours to achieve sealing contact of the elastic sealing ring to the housing parts.
Such screw-type connection of the housing parts with end portions of the housing parts being inserted into each other increases the outer circumferential dimensions of the housing since the overlapping end portions inserted into each other double the wall thickness and provide for a stepped contour of the interior space, thus wasting a part of the interior space.
It is also known to give the end portions of housing parts the same diameter and to connect the two end portions with end surfaces lying onto each other, thereby forming a butt joint of the housing parts. For example, document US 2007-0217199 shows a light-based dermal treatment apparatus comprising an outer shell consisting of two substantially tubular shell parts having end surface butting against each other. However, such known housing configuration is difficult in terms of sealing the housing parts and making the housing waterproof. US 2007-0217199 therefore suggests to connect the two housing parts by means of welding the parts together or using adhesive to glue the housing part together. Such connection, however, is of course disadvantageous since it is no longer possible to open the housing so as to, for example, change the batteries. Moreover, to bring the two housing parts into alignment with each other and to position the end surfaces onto each other, the document suggests to additionally use an inner shell forming a second interior housing what contravenes the desire to reduce the outer dimensions of the housing as far as possible for a drive unit of a given size to be received in the housing.
It is a desire to provide an improved handle of an electrical appliance for personal use, which avoids disadvantages of the prior art and in particular provides further improvements thereof. In particular, it is desired to provide maximum interior space in both housing parts without sacrificing waterproof sealing that can be opened easily.